Pneumatic actuator

ABSTRACT

A pneumatic actuator ( 100 ) is provided according to the invention. The actuator ( 100 ) comprises an actuator body ( 102 ) and a piston rod ( 108 ) extending from the actuator body ( 102 ). The piston rod ( 108 ) moves over an actuation span. The actuation span comprises a first stroke span that is traversed by the piston rod ( 108 ) at a first actuation speed and a second stroke span that is traversed at a second actuation speed that is substantially slower than the first actuation speed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an actuator, and more particularly, toa pneumatic actuator.

2. Statement of the Problem

An actuator is a device that performs some mechanical action. Oneactuator is a piston, wherein a plunger of the piston moves in areciprocating manner. The plunger can therefore be connected to somemanner of work piece or other mechanical system.

In some actuator applications, it is desirable to have more than oneactuation speed and/or more than one actuation force over the range ofmotion of the actuator. For example, in a spot welder machine, a pair ofwelding jaws must be brought together onto a work piece during a weldingoperation. The jaws must clamp onto the work piece with a desired force.Therefore, at the end of a clamping motion range, a relatively highactuation force must be provided to the welding jaws. However, anactuator that provides a high level of force typically provides arelatively small range of actuation travel. This can be a problem wherethe jaws of the spot welder machine must open wide in order to bepositioned on the work piece. Therefore, a jaw actuator of the spotwelder machine needs to move relatively rapidly during a first actuationspan and a large force is not required. During the second actuationspan, the jaws need to move only a small distance, but must be able toprovide a large clamping force.

SUMMARY OF THE INVENTION

A pneumatic actuator is provided according to an embodiment of theinvention. The actuator comprises an actuator body and a piston rodextending from the actuator body. The piston rod moves over an actuationspan. The actuation span comprises a first stroke span that is traversedby the piston rod at a first actuation speed and a second stroke spanthat is traversed at a second actuation speed that is substantiallyslower than the first actuation speed.

A pneumatic is provided according to an embodiment of the invention. Theactuator comprises an actuator body and a piston rod extending from theactuator body. The piston rod moves over an actuation span. Theactuation span comprises a first stroke span that is traversed by thepiston rod using a first actuation force and a second stroke span thatis traversed using a second actuation force that is substantiallygreater than the first actuation force.

A pneumatic is provided according to an embodiment of the invention. Theactuator comprises an actuator body including an outer shell and aninner shell, a piston slidably located in a piston chamber in the innershell, and a ram slidably located in the outer shell and configured tomove at least partially into the inner shell. The actuator furthercomprises a movable ring slidably located in a ring chamber locatedbetween the inner shell and the outer shell and a hydraulic fluidlocated in a region between the ram, the piston, and the movable ring.Upward movement of the movable ring forces the piston downward over afirst stroke span due to movement of a first volume of the hydraulicfluid from the ring chamber into the piston chamber. Downward movementof the ram forces a second volume of the hydraulic fluid down into thepiston chamber, wherein the downward movement of the ram forces thepiston downward over a second stroke span.

ASPECTS OF THE INVENTION

In one embodiment of the actuator, the second stroke span issubstantially smaller in length that the first stroke span.

In another embodiment of the actuator, the first stroke span istraversed by the piston rod at a first actuation speed and the secondstroke span is traversed by the piston rod at a second actuation speedthat is substantially slower than the first actuation speed.

In yet another embodiment of the actuator, the first stroke span istraversed by the piston rod using a first actuation force and the secondstroke span is traversed by the piston rod using a second actuationforce that is substantially greater than the first actuation force.

In yet another embodiment of the actuator, the second stroke span occursat any point along the actuation span.

In yet another embodiment of the actuator, the second stroke span isgenerated by a force multiplier of the actuator.

In yet another embodiment of the actuator, the actuator furthercomprises a plurality of pneumatic ports in the actuator body.

In yet another embodiment of the actuator, the actuator furthercomprises a port A that introduces pressurized gas into the ring chamberbelow the movable ring.

In yet another embodiment of the actuator, the actuator furthercomprises a port B that introduces pressurized gas into the ram chamberbelow the ram.

In yet another embodiment of the actuator, the actuator furthercomprises a port C that introduces pressurized gas into the ram chamberabove the ram.

In yet another embodiment of the actuator, the actuator furthercomprises a port D that introduces pressurized gas into the pistonchamber below the piston.

In yet another embodiment of the actuator, the actuator furthercomprises a piston ring located in the outer shell and below the piston,with the piston ring slidably located in the outer shell and beingconfigured to sealingly slide on the piston rod, wherein a port E islocated below the piston ring and the piston ring moves up and pushesthe piston upward when pressurized gas is introduced into port E.

In yet another embodiment of the actuator, the actuator furthercomprises one or more hydraulic fluid passages extending between the ramthroat and the ring chamber.

DESCRIPTION OF THE DRAWINGS

The same reference number represents the same element on all drawings.It should be understood that the drawings are not necessarily to scale.

FIG. 1 shows a pneumatic actuator according to an embodiment of theinvention.

FIGS. 2A-2C show the actuator in different extension positions.

FIG. 3 shows the actuator in a partial actuation position.

FIG. 4 shows the actuator when a force multiplier has been actuated.

FIG. 5 shows the actuator after the force multiplier has beende-activated.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1-5 and the following description depict specific examples toteach those skilled in the art how to make and use the best mode of theinvention. For the purpose of teaching inventive principles, someconventional aspects have been simplified or omitted. Those skilled inthe art will appreciate variations from these examples that fall withinthe scope of the invention. Those skilled in the art will appreciatethat the features described below can be combined in various ways toform multiple variations of the invention. As a result, the invention isnot limited to the specific examples described below, but only by theclaims and their equivalents.

FIG. 1 shows a pneumatic actuator 100 according to an embodiment of theinvention. The figure comprises a section view approximately along acenter of the actuator 100, showing internal components. The actuator100 includes an actuator body 102 and a piston rod 108 extending out ofthe actuator body 102. The actuator body 102 in one embodiment comprisesan outer shell 101, a top plug 103, a bottom plug 104, and one or morefasteners 106 that hold the top plug 103 and the bottom plug 104 in theouter shell 101. The piston rod 108 movably extends from the bottom plug104, with the piston rod 108 configured to be extended and retracted.The extension and retraction of the piston rod 108 can performmechanical work and the piston rod 108 can be coupled to any manner ofmechanical device. The pneumatic actuator 100 can extend and retract thepiston rod 108 according to selective introduction of a pressurized gas,such as pressurized air.

FIGS. 2A-2C show the actuator 100 in different extension positions. Theactuator 100 in one embodiment comprises a three-position actuator. InFIG. 2A, the piston rod 108 is fully retracted. In FIG. 2B, the pistonrod 108 is extended to a first stroke span. In FIG. 2C, the piston rod108 is fully extended over an actuation (i.e., full stroke) span. Theactuation span therefore comprises the first stroke span plus a secondstroke span. The second stroke span can differ from the first strokespan. For example, the second stroke span can be substantially smallerin length than the first stroke span. This is desirable when actuating amechanical device that requires a large actuation span followed by asmall actuation span, or vice versa.

The first stroke span can be traversed at a first actuation speed andthe second stroke span can be traversed at a second actuation speed. Inone embodiment, the second actuation speed is substantially slower thanthe first actuation speed.

The first stroke span can be traversed using a first actuation force andthe second stroke span can be traversed using a second actuation force.In one embodiment, the second actuation force is substantially greaterthan the first actuation force.

The actuator 100 in one embodiment includes a force amplifier. In oneembodiment, the actuator 100 includes a hydro-pneumatic force amplifier.The force amplifier can provide a force greater than a force generatedby a supplied pneumatic pressure alone. The actuator 100 in oneembodiment can provide a force amplifier at any point in the overallactuation span. The force amplifier can be actuated at a midpoint of theactuation span or can be actuated before or after the midpoint.

Referring again to FIG. 1, the actuator 100 further includes a piston120 that reciprocally moves in a piston chamber 126. The piston 120 isconnected to and moves the piston rod 108.

The actuator 100 further includes an inner shell 109, a lower inner plug131, and an upper inner plug 135. The inner shell 109 forms the pistonchamber 126. The lower inner plug 131 is located at a bottom region ofthe piston chamber 126 and the upper inner plug 135 is located at a topregion of the piston chamber 126. In addition, the lower inner plug 131and the upper inner plug 135 hold the inner shell 109 substantially inposition within the outer shell 101. In one embodiment, the inner shell109 is substantially coaxial with the outer shell 101. The upper innerplug 135 includes an upper inner plug seal(s) 136 that substantiallyseal the upper inner plug 135 to the outer shell 101. In addition, theupper inner plug 135 includes hydraulic fluid passages 137, a ram throat138, and ram throat seals 139. The ram throat 138 receives a ram 160,with the ram throat seals 139 sealing the ram 138 to the upper innerplug 135. As a consequence, the ram 138 blocks the ram throat 138 andcan move reciprocally up and down in the ram throat 138.

The actuator 100 further includes a piston ring 110. The piston ring 110can include piston ring seals 112. The piston ring 110 can move withrespect to the outer shell 101 and can move with respect to the pistonrod 108. The piston ring 110 can move under influence of pressurized gasabove and below the piston ring 110. The pressurized gas can beintroduced and exhausted from above and below the piston ring 110 byport D and port E, respectively.

The actuator 100 further includes a movable ring 140 located in a ringchamber 147 formed between the inner shell 109 and the outer shell 102.The upper side of the movable ring 140 contacts a hydraulic fluid, whichis also present in the piston chamber 126 above the piston 120. Themovable ring 140 is configured to move reciprocally up and down betweenthe outer shell 101 and the inner shell 109 in response to gasintroduced and exhausted by port A. The movable ring 140 can includemovable ring seals 144. The movable ring seals 144 substantially sealthe movable ring 140 to the outer shell 101. In addition, the movablering seals 144 substantially seal the movable ring 140 to the innershell 109.

The actuator 100 further includes the ram 160. The ram 160 movesreciprocally up and down in a ram chamber 161. The ram 160 includes ramseals 163, a ram conduit(s) 163, and a ram filling cavity 166. The ramfilling cavity 166 is fed pressurized gas by a pipe 170 that extendsfrom the top plug 103 and that is connected to port B. The gas istransferred to a portion of the ram chamber 161 below the ram 160, withthe gas traveling through the ram conduit(s) 163 to the portion of theram chamber 161. In addition, the ram 160 is in communication with portC. As a result, the ram 160 can be moved down by introduction ofpressurized gas into port C and can be moved up by introduction ofpressurized gas into port B.

Upward movement of the movable ring 140 forces the piston 120 downwardover a first stroke span due to movement of a first volume of thehydraulic fluid from the ring chamber 147 into the piston chamber 126.Downward movement of the ram 160 forces a second volume of the hydraulicfluid down into the piston chamber 126, wherein the downward movement ofthe ram 160 forces the piston 120 downward over a second stroke span.

The figure shows the actuator 100 in a fully retracted position, wherethe piston rod 108 is fully retracted within the actuator 100.Pressurized gas can be supplied into port D to move the piston 120 to(and hold the piston 120 in) the fully retracted position.Correspondingly, port A, port B, and port C are released in order toallow the piston 120 and the ram 160 to move to fully retracted upwardpositions. As the piston 120 is moved upwards, the hydraulic fluid abovethe piston 120 is moved out of the piston chamber 126 and is forced intothe chamber between the outer shell 101 and the inner shell 109, pushingthe movable ring 140 fully downward. As a result, gas is forced out ofport A. In addition, port C is released and the gas between the ram 160and the top plug 103 is not held. As a result, the upward movement ofthe piston 120 causes the ram 160 to move fully upward.

FIG. 3 shows the actuator 100 in a partial actuation position. Gas hasbeen supplied into port A, pushing the movable ring 140 upward. However,it should be noted that the movable ring 140 has not been moved to itsupward limit. The upward movement of the movable ring 140 forceshydraulic fluid through the hydraulic fluid passage(s) 137 from the ringchamber 147 and into the piston chamber 126, moving the piston 120partially down. Due to the larger diameter of the outer shell 101 andthe consequent volume between the inner shell 109 and the outer shell101, the movement of the movable ring 140 causes the piston 120 to moverelatively rapidly downward (i.e., the first actuation speed). Duringdownward movement of the piston 120, gas is released from the pistonchamber 126 below the piston 120 via port D. The movement of the movablering 140 therefore causes the piston 120 to move over the first (large)stroke span (see FIG. 2B).

FIG. 4 shows the actuator 100 when a force multiplier has been actuated.The force multiplier actuation causes the piston 120 to move over asecond (small) stroke span (see FIG. 2B). However, it should be notedthat the piston rod 108 is not fully extended in this figure, as themovable ring 140 is not in a fully upward position.

To actuate the force multiplier, port B is released, the pressure atport A is held, and pressurized gas is further supplied to port C. Thismoves the ram 160 downward in the ram chamber 161, moving the ram 160fully into the ram throat 138. As a result, the ram 160 blocks off thehydraulic fluid passage(s) 137 and consequently seals the hydraulicfluid in the piston chamber 126. The volume of hydraulic fluid displacedby the ram 160 in the ram throat 138 causes the piston 120 to moveadditionally downward. The large cross-sectional area of the top of theram 160, combined with the smaller cross-sectional area of the bottom ofthe ram 160, provides the force multiplier effect. The ram 160 pressesthe hydraulic fluid into the piston chamber 126. The force at the end ofthe ram 160 in one embodiment is about 6 times the force on the upperside of the ram 160. No additional hydraulic fluid needs to be providedto the actuator 100. The ram 160 therefore provides a large secondactuation force over the second (small) stroke span.

It should be understood that the force multiplier can be actuated at anypoint in the first (large) stroke span. As a result, even if the pistonrod 108 is only at a midpoint of the first stroke span, the ram 160 canbe moved downward and the second (small) stroke span can be traversed bythe piston rod 108, in addition to any portion of the first stroke spanalready traversed.

The retraction operation is essentially the opposite of the extensionoperation. For retraction, the pressurized gas at port A and port C isreleased. Subsequently, pressurized gas is supplied to port B, movingthe ram 160 upward to a fully retracted position. The retraction of theram 160 unblocks the hydraulic fluid passage(s) 137, allowing hydraulicfluid to move from the piston chamber 126 to the ring chamber 147. Then,pressurized gas is introduced to port E in order to force the pistonring 110 fully upward, thereby forcing the piston 120 partially upward(see FIG. 5 and the accompanying discussion below). Pressurized gas isthen introduced to port D (while pressure is held at port E), with thepressurized gas at port D pushing the piston 120 fully upward andforcing the movable ring 140 fully downward. Therefore, the second(small) stroke span is retracted first and then the first (large) strokespan is retracted. Optionally, the pressurized gas at port E can then bereleased, allowing the piston ring 110 to drop down onto the bottom plug104.

FIG. 5 shows the actuator 100 after the force multiplier has beende-activated. Here, port C has been released and pressurized gas hasbeen supplied to port B. As a result of the pressurized gas at port B,the ram 160 has been moved upward, unblocking the ram throat 138 and thehydraulic fluid passage(s) 137. Hydraulic fluid can now pass from thepiston chamber 126 to the ring chamber 147 via the hydraulic fluidpassage(s) 137. In addition, port D remains released and pressurized gashas been supplied at port E. The pressurized gas at port E moves thepiston ring 110 upward. The piston ring 110 comes into contact with thepiston 120, forcing the piston 120 and the piston rod 108 upward. As aconsequence, the piston 120 has moved back upward (i.e., retracted) overthe second (small) stroke span, and at least partially over the first(large) stroke span. Consequently, the movable ring 140 has movedpartially downward. At this point in the retraction sequence,pressurized gas can be maintained at port E and pressurized gas can nowbe supplied to port D, wherein the pressurized gas supplied to port Dwill cause the piston 120 to move fully upward and the piston rod 108will traverse the large stroke span and fully retract.

The pneumatic pressure coupler according to the invention can beemployed according to any of the embodiments in order to provide severaladvantages, if desired. The invention provides an actuation spanincluding first and second stroke spans, where the first and secondstroke spans can be of different lengths. The invention provides anactuation span including first and second actuation speeds. Theinvention provides an actuation span including first and secondactuation forces. The invention provides an actuator including a forcemultiplier. The invention provides an actuator including ahydro-pneumatic force multiplier. The invention provides an actuatorincluding a force multiplier that can be actuated at any point in afirst stroke span.

Advantageously, in the actuator according to the invention, no biasingsprings are required. In the actuator according to the invention, nohydraulic fluid is supplied to the actuator. In the actuator accordingto the invention, force amplification is achieved using only pneumaticinputs.

1. A pneumatic actuator (100) comprising an actuator body (102) and apiston rod (108) extending from the actuator body (102), with the pistonrod (108) moving over an actuation span and with the actuation spanbeing characterized by: a first stroke span that is traversed by thepiston rod (108) at a first actuation speed; and a second stroke spanthat is traversed at a second actuation speed that is substantiallyslower than the first actuation speed.
 2. The actuator (100) of claim 1,with the second stroke span being substantially smaller in length thanthe first stroke span.
 3. The actuator (100) of claim 1, with the firststroke span being traversed by the piston rod (108) using a firstactuation force and with the second stroke span being traversed by thepiston rod (108) using a second actuation force that is substantiallygreater than the first actuation force.
 4. The actuator (100) of claim1, with the second stroke span occurring at any point along theactuation span.
 5. The actuator (100) of claim 1, with the second strokespan being generated by a force multiplier of the actuator (100).
 6. Theactuator (100) of claim 1, further comprising: an actuator body (102)comprising an outer shell (101) and an inner shell (109); a piston (120)slidably located in a piston chamber (126) in the inner shell (109); aram (160) slidably located in the outer shell (101) and configured tomove at least partially into the inner shell (109); a movable ring (140)slidably located in a ring chamber (147) located between the inner shell(109) and the outer shell (101); a hydraulic fluid located in a regionbetween the ram (160), the piston (120), and the movable ring (140);wherein upward movement of the movable ring (140) forces the piston(120) downward over a first stroke span due to movement of a firstvolume of the hydraulic fluid from the ring chamber (147) into thepiston chamber (126); and wherein downward movement of the ram (160)forces a second volume of the hydraulic fluid down into the pistonchamber (126), wherein the downward movement of the ram (160) forces thepiston (120) downward over a second stroke span.
 7. The actuator (100)of claim 6, further comprising a plurality of pneumatic ports in theactuator body (102).
 8. The actuator (100) of claim 6, furthercomprising a port A that introduces pressurized gas into the ringchamber (147) below the movable ring (140).
 9. The actuator (100) ofclaim 6, further comprising a port B that introduces pressurized gasinto the ram chamber (161) below the ram (160).
 10. The actuator (100)of claim 6, further comprising a port C that introduces pressurized gasinto the ram chamber (161) above the ram (160).
 11. The actuator (100)of claim 6, further comprising a port D that introduces pressurized gasinto the piston chamber (126) below the piston (120).
 12. The actuator(100) of claim 6, further comprising a piston ring (110) located in theouter shell (101) and below the piston (120), with the piston ring (110)slidably located in the outer shell (101) and being configured tosealingly slide on the piston rod (108), wherein a port E is locatedbelow the piston ring (110) and the piston ring (110) moves up andpushes the piston (120) upward when pressurized gas is introduced intoport E.
 13. The actuator (100) of claim 6, further comprising one ormore hydraulic fluid passages (137) extending between the ram throat 138and the ring chamber (147).
 14. A pneumatic actuator (100) comprising anactuator body (102) and a piston rod (108) extending from the actuatorbody (102), with the piston rod (108) moving over an actuation span andwith the actuation span being characterized by: a first stroke span thatis traversed by the piston rod (108) using a first actuation force; anda second stroke span that is traversed using a second actuation forcethat is substantially greater than the first actuation force.
 15. Theactuator (100) of claim 14, with the second stroke span beingsubstantially smaller in length than the first stroke span.
 16. Theactuator (100) of claim 14, with the first stroke span being traversedby the piston rod (108) at a first actuation speed and with the secondstroke span being traversed by the piston rod (108) at a secondactuation speed that is substantially slower than the first actuationspeed.
 17. The actuator (100) of claim 14, with the second stroke spanoccurring at any point along the actuation span.
 18. The actuator (100)of claim 14, with the second stroke span being generated by a forcemultiplier of the actuator (100).
 19. The actuator (100) of claim 14,further comprising: an actuator body (102) including an outer shell(101) and an inner shell (109); a piston (120) slidably located in apiston chamber (126) in the inner shell (109); a ram (160) slidablylocated in the outer shell (101) and configured to move at leastpartially into the inner shell (109); a movable ring (140) slidablylocated in a ring chamber (147) located between the inner shell (109)and the outer shell (101); a hydraulic fluid located in a region betweenthe ram (160), the piston (120), and the movable ring (140); whereinupward movement of the movable ring (140) forces the piston (120)downward over a first stroke span due to movement of a first volume ofthe hydraulic fluid from the ring chamber (147) into the piston chamber(126); and wherein downward movement of the ram (160) forces a secondvolume of the hydraulic fluid down into the piston chamber (126),wherein the downward movement of the ram (160) forces the piston (120)downward over a second stroke span.
 20. The actuator (100) of claim 19,further comprising a plurality of pneumatic ports in the actuator body(102).
 21. The actuator (100) of claim 19, further comprising a port Athat introduces pressurized gas into the ring chamber (147) below themovable ring (140).
 22. The actuator (100) of claim 19, furthercomprising a port B that introduces pressurized gas into the ram chamber(161) below the ram (160).
 23. The actuator (100) of claim 19, furthercomprising a port C that introduces pressurized gas into the ram chamber(161) above the ram (160).
 24. The actuator (100) of claim 19, furthercomprising a port D that introduces pressurized gas into the pistonchamber (126) below the piston (120).
 25. The actuator (100) of claim19, further comprising a piston ring (110) located in the outer shell(101) and below the piston (120), with the piston ring (110) slidablylocated in the outer shell (101) and being configured to sealingly slideon the piston rod (108), wherein a port E is located below the pistonring (110) and the piston ring (110) moves up and pushes the piston(120) upward when pressurized gas is introduced into port E.
 26. Theactuator (100) of claim 19, further comprising one or more hydraulicfluid passages (137) extending between the ram throat (138) and the ringchamber (147).
 27. A pneumatic actuator (100), comprising: an actuatorbody (102) comprising an outer shell (101) and an inner shell (109); apiston (120) slidably located in a piston chamber (126) in the innershell (109); a ram (160) slidably located in the outer shell (101) andconfigured to move at least partially into the inner shell (109); amovable ring (140) slidably located in a ring chamber (147) locatedbetween the inner shell (109) and the outer shell (101); a hydraulicfluid located in a region between the ram (160), the piston (120), andthe movable ring (140); wherein upward movement of the movable ring(140) forces the piston (120) downward over a first stroke span due tomovement of a first volume of the hydraulic fluid from the ring chamber(147) into the piston chamber (126); and wherein downward movement ofthe ram (160) forces a second volume of the hydraulic fluid down intothe piston chamber (126), wherein the downward movement of the ram (160)forces the piston (120) downward over a second stroke span.
 28. Theactuator (100) of claim 27, with the first stroke span being traversedby the piston rod (108) using a first actuation force and with thesecond stroke span being traversed by the piston rod (108) using asecond actuation force that is substantially greater than the firstactuation force.
 29. The actuator (100) of claim 27, with the firststroke span being traversed by the piston rod (108) at a first actuationspeed and with the second stroke span being traversed by the piston rod(108) at a second actuation speed that is substantially slower than thefirst actuation speed.
 30. The actuator (100) of claim 27, with thesecond stroke span occurring at any point along the actuation span. 31.The actuator (100) of claim 27, with the second stroke span beinggenerated by a force multiplier of the actuator (100).
 32. The actuator(100) of claim 27, further comprising a plurality of pneumatic ports inthe actuator body (102).
 33. The actuator (100) of claim 27, furthercomprising a port A that introduces pressurized gas into the ringchamber (147) below the movable ring (140).
 34. The actuator (100) ofclaim 27, further comprising a port B that introduces pressurized gasinto the ram chamber (161) below the ram (160).
 35. The actuator (100)of claim 27, further comprising a port C that introduces pressurized gasinto the ram chamber (161) above the ram (160).
 36. The actuator (100)of claim 27, further comprising a port D that introduces pressurized gasinto the piston chamber (126) below the piston (120).
 37. The actuator(100) of claim 27, further comprising a piston ring (110) located in theouter shell (101) and below the piston (120), with the piston ring (110)slidably located in the outer shell (101) and being configured tosealingly slide on the piston rod (108), wherein a port E is locatedbelow the piston ring (110) and the piston ring (110) moves up andpushes the piston (120) upward when pressurized gas is introduced intoport E.
 38. The actuator (100) of claim 27, further comprising one ormore hydraulic fluid passages (137) extending between the ram throat(138) and the ring chamber (147).